Thursday, December 9, 2010

Update for Fri, Dec 10, 2010

Well, we have now been sitting here every day since Nov 28 and still have not been able to launch the rocket. Most days, the strong winds in the vicinity of the launcher are the problem (like today!!!). Some other days, the solar wind just doesn't cooperate and we don't get aurora in the region where we can fly over it with the rocket. Patience...

The solar wind speed has been ok (near 400 km/s) but the density is not very high (1/cc) and its magnetic field is fairly weak. Scientifically, it has been moderately interesting. There is a coronal hole (seen as a huge dark spot in the middle of the sun) and we should start seeing its effects within the next day or so. We would see this as a period of much higher speeds in the solar wind. By the way, at normal solar wind speeds it takes about 4 days for the solar wind to get to Earth from the sun. This so-called High-Speed Stream would get to us about twice as fast.

It might be useful to talk about magnetic fields of planets at this point. Remember, magnetic fields always have a particular direction - this is true of any magnetic field. Also, I should point out that electrically charged particles (i.e., particles that make up the solar wind) cannot generally move ACROSS magnetic fields, although they can easily move ALONG a magnetic field.

So, what does this mean in space? It turns out that Earth's magnetic field is very important to life on this planet. So far, I have been talking about the solar wind, which includes most of the stuff that the sun emits. Aside from the solar wind, though, the sun sometimes emits "solar energetic particles" or SEPs. The radiation that comes with these particles could be hazardous to life on Earth if it wasn't for the fact that Earth's magnetic field prevents them from getting to the ground. In some sense, our magnetic field shields us from these particles.

Here is a movie that gives you an idea of how Earth's magnetic field shields us from the solar wind and, in response, is pushed around by it -- producing aurora in the process:

There is another effect that is important, too. Our atmosphere extends up to about 100 km in altitude, more or less, but our magnetic field reaches way out beyond this altitude and prevents the solar wind from hitting our upper atmosphere directly. If we did not have a magnetic field, the solar wind would constantly be blowing against our atmosphere and there are theories that say the solar wind would gradually drag the atmosphere away from Earth. In fact, some people believe that Mars originally had an atmosphere and a magnetic field, but that the magnetic field became very weak, letting the solar wind drag its atmosphere away (the idea of a magnetic field becoming weaker is not so mysterious).

So, these are some reasons why our magnetic field is so important to us. There are others, too, like the fact that some birds have internal compasses and use the magnetic field to navigate when they migrate, etc.

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